Cleaving pre-fusion state sars-cov-2 spike protein

ABSTRACT

Disclosed is producing recombinant SARS-CoV-2 spike protein in a pre-fusion state, using furin knock out or knockdown mammalian cells (such as HEK293, CHO or other mammalian cells) and using them to generate antibodies and related binding agents. The antibodies/binding agents can be used in SARS-CoV-2 detection assays or in diagnosis of active or prior infection with SARS-CoV-2; in prophylaxis or as a therapeutic; or for prophylactic or therapeutic use against coronaviruses related to SARS-CoV-2.

SEQUENCE LISTING STATEMENT

The instant application contains a Sequence Listing which has been submitted electronically in ASCII format and is hereby incorporated by reference in its entirety.

BACKGROUND

For the coronavirus SARS-CoV-2, which is responsible for the COVID-19 pandemic, only limited treatment options having limited efficacy are available. It is known to primarily enter human cells by binding of its spike protein to the receptor angiotensin converting enzyme 2 (ACE2).

SARS-CoV-2 has four structural proteins, known as the S (spike), E (envelope), M (membrane), and N (nucleocapsid) proteins. The N protein holds the RNA genome, and the S, E, and M proteins together create the viral envelope. The spike (“5”) protein is responsible for allowing the virus to attach to and fuse with the membrane of a host cell.

The S protein is a class I fusion protein; which are known to exist as trimers in their pre-fusion and post-fusion states. The S protein 51 subunit mediates cellular attachment, and the S2 subunit is involved in fusion which allows viral genome entry into the cell. The S protein has two states, a pre-fusion state and a mature/active form, achieved after proteolytic cleavage and activation.

Recombinant SARS-CoV-2 structural proteins are essential for antibody, vaccine and drug development. Recombinant wild-type S-ECD (extracellular domain) is challenging to produce and very unstable. Most of the recombinant S-ECDs on the market contain a mutation to avoid protease cleavage, making the recombinant version different from wild-type and potentially less useful in research or therapy.

Proteolytic cleavage of the S protein can occur in the constitutive secretory pathway of infected cells or during viral entry into target cells, and is essential for viral infectivity.

Furin is a processing enzyme that cleaves substrate proteins into their mature/active forms. Substrates of furin include blood clotting factors, serum proteins and growth factor receptors as well as the viral spike proteins. Furin belongs to the subtilisin-like proprotein convertase family. The members of this family are proprotein convertases that process latent precursor proteins into their biologically active products. Furin is enriched in the Golgi apparatus, where it functions to cleave other proteins into their mature/active forms. Furin is believed to be one of the proprotein convertases for the S protein.

Therefore, inhibition or disruption of cleavage of the S protein by furin may allow production of the S protein in a pre-fusion state (referred to as S-ECD-PFS). S-ECD-PFS can be used as an antigen to generate antibodies for use in detection assays or in diagnosis, or to generate antibodies and related binding agents to SARS-CoV-2 for use in passive immunization or therapy.

SUMMARY

The invention relates to using furin knock out or knockdown mammalian cells (such as HEK293, CHO or other mammalian cells) which produce recombinant SARS-CoV-2 spike protein in a pre-fusion state, to generate antibodies and related binding agents. An exemplary method of generating S-ECD-PFS and confirming its activity is summarized as follows:

-   -   1. Use a CRISPR Cas9 protocol to knock out the furin gene in         mammalian cells, such as HEK293 cells;     -   2. Transfect expression vectors for the S-ECD gene into the         furin−/− cells;     -   3. Purify recombinant S-ECD-PFS, preferably using a nickel         column; and     -   4. Measure S-ECD-PFS′ bio-activity, for example, by determining         its binding ability to recombinant Human ACE2 in a functional         ELISA.

The recombinant S-ECD-PFS can be used as an antigen to generate antibodies/binding molecules for use in detection assays (e.g., in blood or tissues for transfusion or transplantation) or in diagnosis of active or prior infection with SARS-CoV-2. The recombinant S-ECD-PFS can also be used as an antigen to generate antibodies/binding molecules to SARS-CoV-2 for use in passive immunization or other therapy, against SARS-CoV-2 or the following viruses related to SARS-CoV-2: CoV-ZXC21 (MG772934), SARSCoV (NC_004718.3), SARS-like BM4821(MG772934), HCoV-0C43 (AY391777), HKU9-1 (EF065513), HCoV-NL63 (KF530114.1), HCoV229E (KF514433.1), MERS-CoV (NC019843.3), and HKU1 (NC_006577.2).

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 depicts the domain organization of the SARS-CoV-2 spike protein and illustrates the furin cleavage site.

FIG. 2 illustrates the bands in the gel from proteolytic processing and separation of recombinant S-ECD-PFS when expressed in HEK293.

FIG. 3a illustrates the differences between the furin gene wild type (“WT”) and the knock out gene expressed in HEK293 clones 30-18 and 30-28. The sequences shown are WT, wild type (SEQ ID NO: 1) and KO, knock out (SEQ ID NO: 2), with the WT insert separately shown (SEQ ID NO: 3).

FIG. 3b is a Western blot, showing that furin was not present in the media containing HEK293 clones 30-18 and 30-28 (right-hand column) based on absence of agglutination in the right-hand column following adding a anti-furin antibody to the media, with the left-hand column including cells expressing WT furin, and the second right-hand including anti-actin, as controls.

FIG. 3c is a gel showing S-ECD-PFS as a single major band (col. 2) when expressed in FURIN gene knockout HEK293 cells, with HEK293 cells expressing furin WT (col. 1) as control.

FIG. 4 is a gel showing media fractions (cols. 1-5) from the furin−/− cells, following protein purification with a nickel column.

FIG. 5 shows results from an ACE2 binding ELISA for the recombinant S-ECD-PFS, and for a conventional, currently marketed recombinant S-ECD.

DETAILED DESCRIPTION

The singular forms “a”, “an”, and “the” include plural references unless the context clearly dictates otherwise.

A “binding agent” refers to all antibodies, antibody fragments or derivatives of antibodies as described below, as well as proteins and molecules other than proteins, antibodies and fragments or derivatives of antibodies which target S-ECD-PFS, any of which could be modified and tested to become binding agents with high affinity for S-ECD-PFS, using techniques similar to those described below.

A “conjugate” includes conjugates with antibodies or binding agents or conjugates with S-ECD-PFS, as determined from the context. A conjugate can include fusion proteins and proteins or antibodies conjugated with one or more than one polypeptide or antibody or Binding Agent, nucleic acid or chemical compound or a drug carrier. Alternatively, or in addition, a conjugate can comprise one or more other pharmaceutically active agents or drugs. Examples of such other pharmaceutically active agents or drugs that may be suitable for use in a conjugate (or included in a drug carrier) include antibiotics, known antiviral drugs, cytotoxic drugs, and other antibiotics and drugs known or suspected to inhibit or ameliorate Covid 19 infection, including hydroxychloroquine, zithromycin, Remdesivir™, nitric oxide (encapsulated), Ifenprodil, ribavirin, interferon ß-1a, interferon-α, other interferons, Recombinant Mycobacterium bovis, colchicine, favipiravir, lopinavir, ritonavir, Peginterferon Lambda-1A, and Fenretinide, as well as other antibiotics e.g., doxorubicin, vincristine, cisplatin, daunomycin, methotrexate and other anticancer agents such as toxins (such as diphtheria or ricin), cyclophosphamide and other medications, also can be used. alkylating agents (e.g., cyclophosphamide, melphalan etc.), cytotoxic antibiotics (doxorubicin, epirubicin, bleomycin, mitomycin, methotrexate, capecitabine, gemcitabine, fluorouracil, vinca alkaloids and etoposide (vinblastine, vincristine etc.), platinum compounds (carboplatin, cisplatin, oxaliplatin), taxanes (paclitaxel, docetaxel, etc.), topoisomerase I inhibitors (irinotecan, topotecan, etc.) as well as agents like cyclophosphamide, and combinations thereof. In one embodiment, the composition can comprise one or more polypeptide (antibody), fusion protein, conjugate, nucleic acid, vector, or cell of the invention and one or more other pharmaceutically active agents or drugs.

A “conservative amino acid substitution” is one in which the amino acid residue is replaced with an amino acid residue having a similar side chain Families of amino acid residues having similar side chains have been defined in the art. These families include amino acids with basic side chains (e.g., lysine, arginine, histidine), acidic side chains (e.g., aspartic acid, glutamic acid), uncharged polar side chains (e.g., glycine, asparagine, glutamine, serine, threonine, tyrosine, cysteine), nonpolar side chains (e.g., alanine, valine, leucine, isoleucine, proline, phenylalanine, methionine, tryptophan), beta-branched side chains (e.g., threonine, valine, isoleucine) and aromatic side chains (e.g., tyrosine, phenylalanine, tryptophan, histidine).

A “drug carrier” includes liposomes, polymeric micelles, microspheres and nanoparticles.

The term “linker” refers to a compound or moiety that acts as a molecular bridge to operably link two different molecules (e.g., wherein one portion of the linker binds to a binding agent, and wherein another portion of the linker binds to the other molecule(s) in the conjugate). Linkers include, but are not limited to, chemical chains, chemical compounds (e.g., reagents), amino acids, and the like. The linkers may include, but are not limited to, homobifunctional linkers, hetero-bifunctional linkers, biostable linkers, and biodegradable linkers. The linker may be non-planar (e.g., so that the bound components in the conjugate are not rigidly fixed). Heterobifunctional linkers, contain one end having a first reactive functionality to specifically link a first molecule, and an opposite end having a second reactive functionality to specifically link to a second molecule. Depending on such factors as the molecules to be linked, and the conditions in which the linking is performed, the linker may vary in length and composition for optimizing such properties as preservation of biological function stability, resistance to certain chemical and/or temperature parameters, and of sufficient stereo-selectivity or size. Preferably the linker is a “synthetic peptidic linker” that is designated to be rich in glycine, glutamine, and/or serine residues. These residues are arranged e.g. in small repetitive units of up to five amino acids. This small repetitive unit may be repeated for two to five times to form a multimeric unit. At the amino- and/or carboxy-terminal ends of the multimeric unit up to six additional arbitrary, naturally occurring amino acids may be added.

The term S-ECD-PFS refers to SEQ ID NO: 16 and in the context of preparation of antibodies/binding agents for therapy, prophylaxis or in detection assays, is to be read as including other related proteins used in the same way as such antibodies/binding agents, including antibodies/binding agents made using the techniques described herein against any of: CoV-ZXC21 (MG772934), SARSCoV (NC_004718.3), SARS-like BM4821(MG772934), HCoV-0C43 (AY391777), HKU9-1 (EF065513), HCoV-NL63 (KF530114.1), HCoV229E (KF514433.1), MERS-CoV (NC019843.3), HKU1 (NC_006577.2).

The term “sequence identity” refers to the identical amino acids in two sequences compared; such that they can range from 0 to 100% sequence identity. In some embodiments, the sequence identity of a related protein can be about 75%, 80%, 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% sequence identity with S-ECD-PFS or the antibodies/binding agents against it.

Binding Agents

The invention includes antibodies (polyclonal and monoclonal) and other binding agents targeting S-ECD-PFS, administered for diagnosis, prophylaxis or therapy of SARS-CoV-2 or related pathogen infection, or for detection of SARS-CoV-2 or related pathogens in blood units or tissue samples, or in forensic applications, including disease monitoring.

Typically, an antibody has a heavy and light chain. Each heavy and light chain contains a constant region and a variable region (VH and VL, respectively). The regions are also known as “domains.” Light and heavy chain variable regions contain a “framework” region interrupted by three hypervariable regions, also called “complementarity-determining regions” or “CDRs.” The sequences of the framework regions of different light or heavy chains are relatively conserved within a species. The framework region of an antibody, that is the combined framework regions of the constituent light and heavy chains, serves to position and align the CDRs in three dimensional space.

The CDRs are primarily responsible for binding to an epitope of an antigen. The CDRs of each chain are typically referred to as CDR1, CDR2, and CDR3, numbered sequentially starting from the N-terminus, and are also typically identified by the chain in which the particular CDR is located. Thus, a VH CDR3 is located in the variable domain of the heavy chain of the antibody in which it is found, whereas a VL CDR1 is the CDR1 from the variable domain of the light chain of the antibody in which it is found.

In one preferred embodiment, an anti-S-ECD-PFS monoclonal antibody (usually generated in mice or other rodents) or a fragment thereof, is a chimeric, humanized, or human monoclonal antibody. Generally, a humanized antibody has one or more amino acid residues introduced into it from a source that is non-human. These non-human amino acid residues are often referred to as import residues, which are typically taken from an import variable domain. Humanization can be essentially performed following the methods described in Jones et al., Nature 321: 522-525 (1986); Riechmann et al., Nature 332: 323-327 (1988); or Verhoeyen et al., Science 239: 1534-1536 (1988), by substituting rodent CDRs or CDR sequences for the corresponding sequences of a human antibody. Accordingly, such humanized antibodies are chimeric antibodies (U.S. Pat. No. 4,816,567) wherein substantially less than an intact human variable domain has been substituted by the corresponding sequence from a non-human species. In practice, humanized antibodies are typically human antibodies in which some CDR residues and possibly some FR residues are substituted by residues from analogous sites in rodent antibodies.

In some embodiments, “human antibody” refers to an immunoglobulin comprising human hypervariable regions in addition to human framework and constant regions. Such antibodies can be produced using various techniques known in the art. For example in vitro methods involve use of recombinant libraries of human antibody fragments displayed on bacteriophage (e.g., McCafferty et al, 1990, Nature 348: 552-554; Hoogenboom & Winter, J. Mol. Biol. 227: 381(1991); and Marks et al, J. Mol. Biol. 222: 581 (1991)), yeast cells (Boder and Wittrup, 1997, Nat Biotechnol 15: 553-557), or ribosomes (Hanes and Pluckthun, 1997, Proc Natl Acad Sci USA 94: 4937-4942). Similarly, human antibodies can be made by introducing human immunoglobulin loci into transgenic animals, e.g., mice in which the endogenous immunoglobulin genes have been partially or completely inactivated. Upon challenge, human antibody production is observed, which closely resembles that seen in humans in all respects, including gene rearrangement, assembly, and antibody repertoire. This approach is described, e.g., in U.S. Pat. Nos. 6,150,584, 5,545,807; 5,545,806; 5,569,825; 5,625,126; 5,633,425; 5,661,016, and in the following scientific publications: (e.g., Jakobavits, Drug Deliv Rev. 31: 33-42 (1998), Marks et al, Bio/Technology 10: 779-783 (1992); Lonberg et al, Nature 368: 856-859 (1994); Morrison, Nature 368: 812-13 (1994); Fishwild et al, Nature Biotechnology 14: 845-51 (1996); Neuberger, Nature Biotechnology 14: 826 (1996); Lonberg &Huszar, Intern. Rev. Immunol. 13: 65-93 (1995).

In certain embodiments, the antibody or the fragment thereof disclosed herein comprises or is an F(ab)′2, an Fab, an Fv, or a single-chain Fv fragment of the above anti-S-ECD-PFS antibodies.

In some embodiments, “antibody fragments” means molecules that comprise a portion of an intact antibody, generally the antigen binding or variable region of the intact antibody. Examples of antibody fragments include Fab, Fab′, F(ab)′2, and Fv fragments; single domain antibodies (see, e.g., Wesolowski, Med Microbiol Immunol. (2009) 198 (3): 157-74; Saerens, et al., Curr Opin Pharmacol. (2008) 8 (5): 600-8; Harmsen and de Haard, Appl Microbiol Biotechnol. (2007) 77 (1): 13-22)); helix-stabilized antibodies (see, e.g., Arndt et al., J Mol Biol 312: 221-228 (2001); diabodies (see below); single-chain antibody molecules (“scFvs,” see, e.g., U.S. Pat. No. 5,888,773); disulfide stabilized antibodies (“dsFvs”, see, e.g., U.S. Pat. Nos. 5,747,654 and 6,558,672), and domain antibodies (“dAbs,” see, e.g., Holt et al., Trends Biotech 21(11): 484-490 (2003), Ghahroudi et al., FEBS Lett. 414: 521-526 (1997), Lauwereys et al., EMBO J 17: 3512-3520 (1998), Reiter et al., J. Mol. Biol. 290: 685-698 (1999), Davies and Riechmann, Biotechnology, 13: 475-479 (2001)).

U.S. Pat. No. 5,932,448 discloses making of bispecific antibodies with Fab′ portions joined by a leucine zipper; U.S. Pat. No. 7,538,196, discloses making of bispecific antibodies where portions are joined with a linker; U.S. Pat. No. 8,148,496 discloses a multi-specific Fv antibody construct having at least four variable domains which are linked with each other via peptide linkers. A bispecific antibody could have one arm targeting ICB and the other arm targeting a tumor or cancer marker.

US Publ'n No. 20170335281 describes making of a genetically modified T cell expressing a CAR that comprises an antigen binding domain that binds to a cancer associated antigen. The same general techniques can be applied to modify T cells or other immune effector cells to express one or more of CDR1, CDR2 and CDR3 of an antigen binding domain, for cancer treatment. The antigen binding domain of the CAR polypeptide molecule can include any antibody, antibody fragment, an scFv, a Fv, a Fab, a (Fab′)₂, a single domain antibody (SDAB, disclosed in WO 9404678 and Hamers-Casterman, C. et al. (1993) Nature 363:446-448), a VH or VL domain, or a VHH domain. Such CAR expressing T cells could be used in combination with the therapy described herein, or the antigen binding domain could be an anti-S-ECD-PFS domain.

High Affinity Antibody Variants

Making of Anti-S-ECD-PFS Antibodies with High Affinity

Antibodies can be humanized with retention of high affinity for the antigen and other favorable biological properties. To achieve this goal, humanized antibodies are prepared by a process of analysis of the parental sequences and various conceptual humanized products using three-dimensional models of the parental and humanized sequences. Three-dimensional immunoglobulin models are commonly available. Computer programs are available which illustrate and display probable three-dimensional conformational structures of selected candidate immunoglobulin sequences. Inspection of these displays permits analysis of the likely role of the residues in the functioning of the candidate immunoglobulin sequence, i.e., the analysis of residues that influence the ability of the candidate immunoglobulin to bind its antigen. In this way, FR residues can be selected and combined from the recipient and import sequences so that the desired antibody characteristic, such as increased affinity for the target antigen(s), is achieved.

Examples of framework region residues to modify include those which non-covalently bind target directly (Amit et al. Science 233: 747-753 (1986)); interact with/effect the conformation of CDR (Chothia et al. J. Mol. Biol. 196: 901-917 (1987)); and/or participate in the VL-VH interface (EP 239 400 B1). In certain embodiments, modification of one or more of such framework region residues results in an enhancement of the binding affinity of the antibody for the target of interest.

Nucleic acid molecules encoding amino acid sequence variants are prepared by a variety of methods known in the art. These methods include, but are not limited to, oligonucleotide-mediated (or site-directed) mutagenesis, PCR mutagenesis, and cassette mutagenesis of an earlier prepared variant or a non-variant version of the species-dependent antibody. The preferred method for generating variants is an oligonucleotide-mediated synthesis. In certain embodiments, the antibody variant will only have a single hypervariable region residue substituted, e.g. from about two to about fifteen hypervariable region substitutions.

One method for generating the library of variants is by oligonucleotide mediated synthesis. Three oligonucleotides of approximately 100 nucleotides each may be synthesized spanning the entire light chain or heavy chain variable region. Each oligonucleotide may comprise: (1) a 60 amino acid stretch generated by the triplet (NNK)20 where N is any nucleotide and K is G or T, and (2) an approximately 15-30 nucleotide overlap with either the next oligo or with the vector sequence at each end. Upon annealing of these three oligonucleotides in a PCR reaction, the polymerase will fill in the opposite strand generating a complete double stranded heavy chain or light chain variable region sequence. The number of triplets may be adjusted to any length of repeats and their position within the oligonucleotide may be chosen so as to only substitute amino acids in a given CDR or framework region. By using (NNK), all twenty amino acids are possible at each position in the encoded variants. The overlapping sequence of 5-10 amino acids (15-30 nucleotides) will not be substituted, but this may be chosen to fall within the stacking regions of the framework, or may substituted by a separate or subsequent round of synthesis. Methods for synthesizing oligonucleotides are well known in the art and are also commercially available. Methods for generating the antibody variants from these oligonucleotides are also well known in the art, e.g., PCR.

The library of heavy and light chain variants, differing at random positions in their sequence, can be constructed in any expression vector, such as a bacteriophage, each of which contains DNA encoding a particular heavy and light chain variant.

Following production of the antibody variants, the biological activity of variant relative to the parent antibody is determined. As noted above, this involves determining the binding affinity of the variant for the ICB target. Numerous high-throughput methods exist for rapidly screening antibody variants for their ability to bind the target of interest.

One or more of the antibody variants selected from this initial screen may then be screened for enhanced binding affinity relative to the parent antibody. One common method for determining binding affinity is by assessing the association and dissociation rate constants using a BIAcore surface plasmon resonance system (BIAcore, Inc.). A biosensor chip is activated for covalent coupling of the target according to the manufacturer's (BIAcore) instructions. The target is then diluted and injected over the chip to obtain a signal in response units (RU) of immobilized material. Since the signal in RU is proportional to the mass of immobilized material, this represents a range of immobilized target densities on the matrix. Dissociation data are fit to a one-site model to obtain koff+/−s.d. (standard deviation of measurements). Pseudo-first order rate constant (ks) are calculated for each association curve, and plotted as a function of protein concentration to obtain kon+/−s.e. (standard error of fit). Equilibrium dissociation constants for binding, Kd's, are calculated from SPR measurements as koff/kon. Since the equilibrium dissociation constant, Kd, is inversely proportional to koff, an estimate of affinity improvement can be made assuming the association rate (kon) is a constant for all variants.

The resulting candidate(s) with high affinity may optionally be subjected to one or more further biological activity assays to confirm that the antibody variant(s) with enhanced binding affinity still retain the desired therapeutic attributes, as can be tested in the assays described in the figures above. The optimal antibody variant retains the ability to bind the ICB target with a binding affinity significantly higher than the parent antibody. The antibody variant(s) so selected may be subjected to further modifications oftentimes depending upon the intended use of the antibody. Such modifications may involve further alteration of the amino acid sequence, fusion to heterologous polypeptide(s) and/or covalent modifications such as those elaborated below. For example, any cysteine residues not involved in maintaining the proper conformation of the antibody variant may be substituted, generally with serine, to improve the oxidative stability of the molecule and prevent aberrant cross linking. Conversely, (a) cysteine bond(s) may be added to the antibody to improve its stability (particularly where the antibody is an antibody fragment such as an Fv fragment).

Conjugates of Binding Agents

Conjugates of binding agents with any cytotoxic agents, antibiotics, known antiviral drugs, cytotoxic drugs, and other antibiotics and drugs known or suspected to inhibit or ameliorate Covid 19 infection noted above, as well as with drug carriers containing any such cytotoxic agents, antibiotics, etc., can be used in therapy or prophylaxis of Covid 19.

Such binding agents and methods of conjugating the binding agents to a molecule of interest are well known in the art and have been used in the production of antibody conjugates. Some examples of linking groups and conjugation methods are described in US Publication No. 2011/060318 (incorporated by reference). The choice of binding agent, coupling (conjugation) technique and linking group for use in the conjugates described herein is well known.

Binding agents are conjugated via reactive sites on the binding agents via a linking group. For example, primary amino groups present on amino acid residue such as the epsilon amino group of lysine, and the alpha amino group of N-terminal amino acids of proteins can be used as functional groups for conjugation. Often it is desirable to convert one or more primary amino groups of a binding agent to a thiol-containing group (e.g., from a cysteine or homocysteine residue), an electrophilic unsaturated group such as a maleimide group, or halogenated group such as a bromoacetyl group, for conjugation to thiol reactive peptides. Optionally, a primary amino group on the hemagglutinin FIR peptide or on a linker moiety attached to the peptide, can be converted to the thiol-containing group, for coupling with a thiol (sulfhydryl) moiety on the carrier protein, e.g., by a disulfide bond.

In some embodiments, the conjugation can be achieved, for example, by using succinimidyl 4-[N-maleimidomethyl]cyclohexane-1-carboxylate (SMCC), sulfosuccinimidyl 4-(N-maleimidomethyl)cyclohexane-1-carboxylate (sSMCC

-maleimidocaproyloxy]-sulfosuccinimde ester (sEMCS), bis-diazobenzidine (BDB), N-maleimidobenzoyl-N-hydroxysuccinimide ester (MBS), glutaraldehyde, 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDCI), or N-acetyl homocysteine thiolactone (NAHT).

In the SMCC method, SMCC cross-links the SH-group of a cysteine residue to the amino group of a lysine residue on the binding agent. In the SMCC method, the binding agent first is activated by reacting SMCC with a primary amine (e.g., on a lysine residue of the carrier protein). The resulting activated binding agent is then separated from any excess SMCC and by-product therefrom, and a cysteine-containing peptide is added. The thiol group of the cysteine adds across the double bond of the maleimide moiety of the SMCC-derivatized binding agent, thus forming a covalent sulfide bond to couple the binding agent to the peptide. If a hemagglutinin FIR peptide does not include a cysteine residue, then a cysteine residue should be added to the peptide, preferably at the N-terminus or C-terminus. If the epitope portion of the hemagglutinin FIR peptide contains a cysteine or if there is more than one cysteine group in the peptide, then another conjugation technique that does not modify the cysteine residues should be utilized. Since the linkage between the binding agent and the peptide should not interfere with the epitope portion of the peptide, the added cysteine residue optionally can be separated from the hemagglutinin FIR peptide by including one or more amino acid residues as a spacer. The cysteine, spacer residues, and the modified SMCC attached to the binding agent constitute the linking group of the hemagglutinin FIR peptide conjugate.

Another simple coupling of a peptide to a binding agent can be achieved with a carbodiimide crosslinker such as 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC), 1-cyclohexyl-2-(2-morpholinoethyl) carbodiimide metho-p-toluenesulfonate (CMC), and the like to covalently attach carboxyl groups to primary amine groups. This method is simple and provides a relatively random orientation that allows for antibody generation against many possible epitopes. One drawback is that EDC coupling can result in some amount of polymerization. This can decrease the solubility of the conjugate, which can complicate the handling of the material.

Other coupling agents can be used to conjugate the FIR peptide to the binding agent, either directly or via a linking group. For example, conjugation can be achieved using isocyanate coupling agents, such as 2-morpholinoethylisocyanide; N-acetyl homocysteine thiolactone, which can be used to add a thiol group onto a binding agent such as OMPC coupling with a maleimide or bromoacetyl functionalized peptide; or any other agents for coupling haptens (potential immunogens) to polypeptides and proteins, many of which are well known.

Non-specific cross-linking agents and their use are well known in the art. Examples of such reagents and their use include reaction with glutaraldehyde; reaction with N-ethyl-N′-(3-dimethylaminopropyl)carbodiimide, with or without admixture of a succinylated carrier; periodate oxidation of glycosylated substituents followed by coupling to free amino groups of a protein carrier in the presence of sodium borohydride or sodium cyanoborohydride; periodate oxidation of non-acylated terminal serine and threonine residues forming terminal aldehydes which can then be reacted with amines or hydrazides creating a Schiff base or a hydrazone, which can be reduced with cyanoborohydride to secondary amines; diazotization of aromatic amino groups followed by coupling on tyrosine side chain residues of the protein; reaction with isocyanates; or reaction of mixed anhydrides. The linkers can be supplemented and extended with spacer groups, such as additional amino acid residues, adipic acid dihydrazide, and the like.

Typical spacer peptide groups for use in conjugation of the FIR peptide to the binding agent include single amino acids (e.g., Cys) and short peptide sequences (i.e., short non-hemagglutinin FIR peptide sequences) attached to the FIR peptide, e.g., a lysine containing peptide, a cysteine-containing peptide, and the like. Some preferred linking groups comprise a sulfide bond (e.g., as in SMCC and related coupling methods). Some preferred linking groups include a Cys residue bound to the succinimido moiety through the sulfhydryl side chain thereof which is bound the N-terminus of the FIR peptide by a peptide bond. The 1-carbonyl group on the cyclohexyl moiety of Formula I is bound to a primary amine on the binding agent by an amide bond.

In some embodiments, the peptide conjugates include a single hemagglutinin FIR peptide attached to the binding agent, while in other embodiments, two or more hemagglutinin FIR peptides can be attached to the binding agent.

Formulations for In Vivo Use

I. Dosing of the Binding Agents and Other Active Ingredients

1. Formulations

The dosages of binding agents or conjugates for treating or prophylaxis of SARS-CoV2 can be determined as follows. The conjugates can include polyethylene glycol, immunoglobulin Fc fragments, or collagen, albumin and other proteins which are linked to a base molecule, and antibodies (including monoclonal antibodies and fragments thereof). Any composition or compound that can simulate the biological response associated with the binding of ACE-2 receptors can be used. General details on techniques for formulation and administration are well-described in the scientific literature (see, e.g., Remington's Pharmaceutical Sciences, Maack Publishing Co., Easton Pa.).

The formulations containing pharmaceutically active products used in the methods of the disclosure can be formulated for administration in any conventionally acceptable way including, but not limited to, intravenously, subcutaneously, intramuscularly, sublingually, topically, orally and via inhalation. Illustrative examples are set forth below.

When the formulations are delivered by intravenous injection, the formulations containing pharmaceutically active ligands can be in the form of a sterile injectable preparation, such as a sterile injectable aqueous or oleaginous suspension. This suspension can be formulated according to the known art using those suitable dispersing or wetting agents and suspending agents which have been mentioned above. The sterile injectable preparation can also be a sterile injectable solution or suspension in a nontoxic parenterally-acceptable diluent or solvent. Among the acceptable vehicles and solvents that can be employed are water and Ringer's solution, an isotonic sodium chloride. In addition, sterile fixed oils can conventionally be employed as a solvent or suspending medium. For this purpose any bland fixed oil can be employed including synthetic mono- or diglycerides. In addition, fatty acids such as oleic acid can likewise be used in the preparation of injectables.

Pharmaceutical formulations for oral administration can be formulated using pharmaceutically acceptable carriers well known in the art in dosages suitable for oral administration. Such carriers enable the pharmaceutical formulations to be formulated in unit dosage forms as tablets, pills, powder, capsules, liquids, lozenges, gels, syrups, slurries, suspensions, etc., suitable for ingestion by the patient, which would often include an enteric coating to prevent destruction of the ligand in the highly acidic environment of the stomach. Pharmaceutical preparations for oral use can be combinations of ligands with a solid excipient, optionally grinding a resulting mixture, and processing the mixture of granules, after adding suitable additional compounds, if desired, to obtain tablets or pills.

Suitable solid excipients are carbohydrate or protein fillers which include, but are not limited to, sugars, including lactose, sucrose, mannitol, or sorbitol; starch from corn, wheat, rice, potato, or other plants; cellulose such as methyl cellulose, hydroxypropylmethyl-cellulose, or sodium carboxymethylcellulose; and gums including arabic and tragacanth; as well as proteins such as gelatin and collagen. If desired, disintegrating or solubilizing agents may be added, such as the cross-linked polyvinyl pyrrolidone, agar, alginic acid, or a salt thereof, such as sodium alginate. Pharmaceutical preparations that can also be used orally are, for example, push-fit capsules made of gelatin, as well as soft, sealed capsules made of gelatin and a coating such as glycerol or sorbitol. Push-fit capsules can contain ligands mixed with a filler or binders such as lactose or starches, lubricants such as talc or magnesium stearate, and, optionally, stabilizers. In soft capsules, the ligands may be dissolved or suspended in suitable liquids, such as fatty oils, liquid paraffin, or liquid polyethylene glycol with or without stabilizers.

Aqueous suspensions for internal use contain ligands mixed with excipients suitable for the manufacture of aqueous suspensions. Such excipients include a suspending agent, such as sodium carboxymethylcellulose, methylcellulose, hydroxypropylnethylcellulose, sodium alginate, polyvinylpyrrolidone, gum tragacanth and gum acacia, and dispersing or wetting agents such as a naturally occurring phosphatide (e.g., lecithin), a condensation product of an alkylene oxide with a fatty acid (e.g., polyoxyethylene stearate), a condensation product of ethylene oxide with a long chain aliphatic alcohol (e.g., heptadecaethylene oxycetanol), a condensation product of ethylene oxide with a partial ester derived from a fatty acid and a hexitol (e.g., polyoxyethylene sorbitol mono-oleate), or a condensation product of ethylene oxide with a partial ester derived from fatty acid and a hexitol anhydride (e.g., polyoxyethylene sorbitan monooleate). The aqueous suspension can also contain one or more preservatives such as ethyl or n-propyl p-hydroxybenzoate, and other additives as desired, including coloring agents, flavoring agents and sweetening agents, such as sucrose, aspartame or saccharin. Formulations can be adjusted for osmolarity.

Oil suspensions for internal use can be formulated by suspending ligands in a vegetable oil, such as arachis oil, olive oil, sesame oil or coconut oil, or in a mineral oil such as liquid paraffin. The oil suspensions can contain a thickening agent, such as beeswax, hard paraffin or cetyl alcohol. Sweetening agents can be added to provide a palatable oral preparation. These formulations can be preserved by the addition of an antioxidant such as ascorbic acid.

Dispersible powders and granules of the disclosure suitable for preparation of an aqueous suspension by the addition of water can be formulated from ligands in admixture with a dispersing, suspending and/or wetting agent, and one or more preservatives. Suitable dispersing or wetting agents and suspending agents include those disclosed above. Additional excipients, for example sweetening, flavoring and coloring agents, can also be present.

The pharmaceutical formulations can also be in the form of oil-in-water emulsions. The oily phase can be a vegetable oil, such as olive oil or arachis oil, a mineral oil, such as liquid paraffin, or a mixture of these. Suitable emulsifying agents include naturally-occurring gums, such as gum acacia and gum tragacanth, naturally occurring phosphatides, such as soybean lecithin, esters or partial esters derived from fatty acids and hexitol anhydrides, such as sorbitan mono-oleate, and condensation products of these partial esters with ethylene oxide, such as polyoxyethylene sorbitan mono-oleate. The emulsion can also contain sweetening and flavoring agents. Syrups and elixirs can be formulated with sweetening agents, such as glycerol, sorbitol or sucrose. Such formulations can also contain a demulcent, a preservative, a flavoring or a coloring agent.

For intravenous injection, water soluble antibodies can be administered by the drip method, whereby a pharmaceutical formulation containing the formulation and a physiologically acceptable excipients is infused. Physiologically acceptable excipients may include, for example, 5% dextrose, 0.9% saline, Ringer's solution or other suitable excipients.

In one embodiment, the formulation is administered via site-specific or targeted local delivery techniques. Examples of site-specific or targeted local delivery techniques include various implantable depot sources of the antibody or local delivery catheters, such as infusion catheters, an indwelling catheter, or a needle catheter, synthetic grafts, adventitial wraps, shunts, and stents or other implantable devices, site specific carriers, direct injection, or direct application. See, e.g., WO 00/53211 and U.S. Pat. No. 5,981,568.

In another embodiment of the present disclosure, an article of manufacture is provided which contains any of the pharmaceutical compositions and formulations described herein (e.g., comprising a binding agent) and provides instructions for its use and/or reconstitution. The article of manufacture comprises a container. Suitable containers include, for example, bottles, vials (e.g. dual chamber vials), syringes (such as dual chamber syringes) and test tubes. The container may be formed from a variety of materials such as glass or plastic. The container holds the formulation and the label on, or associated with, the container may indicate directions for reconstitution and/or use. For example, the label may indicate that the formulation is reconstituted to particular protein concentrations. The container holding the formulation may be a multi-use vial, which allows for repeat administrations (e.g., from 2-6 administrations) of the reconstituted formulation. The article of manufacture may further comprise a second container comprising a suitable diluent (e.g. BWFI). Upon mixing of the diluent and the lyophilized formulation, the final protein concentration in the reconstituted formulation will generally be at least 50 mg/mL. The article of manufacture may further include other materials desirable from a commercial and user standpoint, including other buffers, diluents, filters, needles, syringes, and package inserts with instructions for use.

2. Administration and Dosing Regimen of the Formulations

The formulations containing pharmaceutically active binding agent and other active ingredients can be administered in any conventionally acceptable way including, but not limited to, by intravenous, intramuscular, intraperitoneal, intracerebrospinal, subcutaneous, intracutaneous, intraarticular, intrasynovial, intrathecal, intradermal, intratumoral, intranodal, intramedulla, oral, inhalation or topical routes; or it may be administered orally, by inhalation spray, topically, rectally, nasally, buccally, vaginally or via an implanted reservoir; and in any case, as a bolus or by continuous infusion over a period of time; or via injectable depot routes of administration such as using 1-, 3-, or 6-month depot injectable or biodegradable materials and methods Administration will vary with the pharmacokinetics and other properties of the drugs and the patient's condition.

Commercially available nebulizers for liquid formulations, including jet nebulizers and ultrasonic nebulizers are useful for administration. Liquid formulations can be directly nebulized and lyophilized powder can be nebulized after reconstitution. Alternatively, binding agents can be aerosolized using a fluorocarbon formulation and a metered dose inhaler, or inhaled as a lyophilized and milled powder.

The subject to be treated by the methods described herein can be a mammal, more preferably a human. Mammals include, but are not limited to, farm animals, sport animals, pets, primates, horses, dogs, cats, mice, and rats.

The amount of binding agent alone or in combination with another agent that is adequate to accomplish this is considered the therapeutically effective dose. The dosing schedule and amounts, i.e., the “dosing regimen,” will depend upon a variety of factors, including the stage of the disease or condition, the severity of the disease or condition, the severity of the adverse side effects, the general state of the patient's health, the patient's physical status, age and the like. In calculating the dosage regimen for a patient, the mode of administration is also taken into consideration. The dosing regimen must also take into consideration the pharmacokinetics, i.e., the rate of absorption, bioavailability, metabolism, clearance, and the like. Based on these values (which are determined in vitro, and in mammalian animal models and extrapolated to humans) the dosing regimen is projected for humans, and is then tested and further refined in clinical trials, in a conventional dose-finding study, as is well-known in the art.

The state of the art allows the clinician to determine the dosing regimen for each individual patient, depending on factors including administration route, disease stage, patient size, and patient level of SARS-CoV2 or related pathogen. For example, a physician may initially use escalating dosages, starting at a particular level, and then titrate the dosage at increments for each individual being treated based on their individual responses. Depending on the subject, the administration of the formulation is maintained for as specific period of time or for as long as needed to effectively treat the subject's symptoms or prevent their occurrence in the first place.

Lyophilized Formulation

After preparation of a suitable binding agent or conjugate, it can be prepared in a formulation for administration to a subject. A lyophilized formulation is especially preferred for the binding agent, which as a first step, requires preparing a pre-lyophilized formulation. The amount of binding agent in the pre-lyophilized formulation is determined taking into account the desired dose volumes, mode(s) of administration etc. The binding agent is generally present in solution. For example, the binding agent may be present in a pH-buffered solution at a pH from about 4-8, and preferably from about 5-7. Exemplary buffers include histidine, phosphate, Tris, citrate, succinate and other organic acids. The buffer concentration can be from about 1 mM to about 20 mM, or from about 3 mM to about 15 mM, depending, for example, on the buffer and the desired isotonicity of the formulation (e.g. of the reconstituted formulation). The preferred buffer is histidine as it can have lyoprotective properties. Succinate is also a useful buffer.

The lyoprotectant is added to the pre-lyophilized formulation. In preferred embodiments, the lyoprotectant is a non-reducing sugar such as sucrose or trehalose. The amount of lyoprotectant in the pre-lyophilized formulation is generally such that, upon reconstitution, the resulting formulation will be isotonic, as preferred, though hypertonic reconstituted formulations may also be suitable. In addition, the amount of lyoprotectant must not be too low such that an unacceptable amount of degradation/aggregation of the Binding Agent occurs upon lyophilization.

Where the lyoprotectant is a sugar (such as sucrose or trehalose) and the binding agent is an antibody, exemplary lyoprotectant concentrations in the pre-lyophilized formulation are from about 10 mM to about 400 mM, and preferably from about 30 mM to 5 about 300 mM, and most preferably from about 50 mM to about 100 mM.

The ratio of binding agent to lyoprotectant is selected for each binding agent and lyoprotectant combination. In the case of an antibody as the binding agent and a sugar (e.g., sucrose or trehalose) as the lyoprotectant for generating an isotonic reconstituted formulation with a high protein concentration, the molar ratio of lyoprotectant to antibody may be from about 100 to about 1500 moles lyoprotectant to 1 mole antibody, and preferably from about 200 to about 1000 moles of lyoprotectant to 1 mole antibody, including from about 200 to about 600 moles of lyoprotectant to 1 mole antibody.

In preferred embodiments, it has been found to be desirable to add a surfactant to the pre-lyophilized formulation. Alternatively, or in addition, the surfactant may be added to the lyophilized formulation and/or the reconstituted formulation. Exemplary surfactants include nonionic surfactants such as polysorbates (e.g. polysorbates 20 or 80); poloxamers (e.g. poloxamer 188); Triton; sodium dodecyl sulfate (SDS); sodium laurel sulfate; sodium octyl glycoside; lauryl-, myristyl-, linoleyl-, or stearyl-sulfobetaine; lauryl-, myristyl-, linoleyl- or stearyl-sarcosine; linoleyl-, myristyl-, or cetyl-betaine; lauroamidopropyl-, cocamidopropyl-, linoleamidopropyl-, myristamidopropyl-, palnidopropyl-, or isostearamidopropyl-betaine (e.g lauroamidopropyl); myristamidopropyl-, palmidopropyl-, or isostearamidopropyl-dimethylamine; sodium methyl cocoyl-, or disodium methyl oleyl-taurate; and the MONAQUAT™ series (Mona Industries, Inc., Paterson, N.J.), polyethyl glycol, polypropyl glycol, and copolymers of ethylene and propylene glycol (e.g. Pluronics, PF68). The amount of surfactant added is such that it reduces aggregation of the reconstituted protein and minimizes the formation of particulates after reconstitution. For example, the surfactant may be present in the pre-lyophilized formulation in an amount from about 0.001-0.5%, and preferably from about 0.005-0.05%.

A mixture of the lyoprotectant (such as sucrose or trehalose) and a bulking agent (e.g. mannitol or glycine) may be used in the preparation of the pre-lyophilization formulation. The bulking agent may allow for the production of a uniform lyophilized cake without excessive pockets therein.

Other pharmaceutically acceptable carriers, excipients or stabilizers such as those described in Remington's Pharmaceutical Sciences 16th edition, Osol, A. Ed. (1980) may be included in the pre-lyophilized formulation (and/or the lyophilized formulation and/or the reconstituted formulation) provided that they do not adversely affect the desired characteristics of the formulation. Acceptable carriers, excipients or stabilizers are nontoxic to recipients at the dosages and concentrations employed and include; additional buffering agents; preservatives; co-solvents; antioxidants including ascorbic acid and methionine; chelating agents such as EDTA; metal complexes (e.g. Zn-protein complexes); biodegradable polymers such as polyesters; and/or salt-forming counterions such as sodium.

The pharmaceutical compositions and formulations described herein are preferably stable, so as to retain its physical and chemical stability and integrity upon storage. Various analytical techniques for measuring protein stability are available in the art and are reviewed in Peptide and Protein Drug Delivery, 247-301, Vincent Lee Ed., Marcel Dekker, Inc., New York, N.Y., Pubs. (1991) and Jones, A. Adv. Drug Delivery Rev. 10: 29-90 (1993). Stability can be measured at a selected temperature for a selected time period.

The formulations to be used for in vivo administration must be sterile. This is readily accomplished by filtration through sterile filtration membranes, prior to, or following, lyophilization and reconstitution. Alternatively, sterility of the entire mixture may be accomplished by autoclaving the ingredients, except for protein, at about 120° C. for about 30 minutes.

After the binding agent and lyoprotectant are mixed together, the formulation is lyophilized. Many different freeze-dryers are available for this purpose such as Hull50® (Hull, USA) or GT20® (Leybold-Heraeus, Germany) freeze-dryers. Freeze-drying is accomplished by freezing the formulation and subsequently subliming ice from the frozen content at a temperature suitable for primary drying. Under this condition, the product temperature is below the eutectic point or the collapse temperature of the formulation.

Typically, the shelf temperature for the primary drying will range from about −30 to 25° C. (provided the product remains frozen during primary drying) at a suitable pressure, ranging typically from about 50 to 250 mTorr. The formulation, size and type of the container holding the sample (e.g., glass vial) and the volume of liquid will mainly dictate the time required for drying, which can range from a few hours to several days (e.g. 40-60 hrs). A secondary drying stage may be carried out at about 0-40° C., depending primarily on the type and size of container and the type of protein employed. For example, the shelf temperature throughout the entire water removal phase of lyophilization may be from about 15-30° C. (e.g., about 20° C.). The time and pressure required for secondary drying will be that which produces a suitable lyophilized cake, dependent, e.g., on the temperature and other parameters. The secondary drying time is dictated by the desired residual moisture level in the product and typically takes at least about 5 hours (e.g. 10-15 hours). The pressure may be the same as that employed during the primary drying step. Freeze-drying conditions can be varied depending on the formulation and vial size.

In some instances, it may be desirable to lyophilize the protein formulation in the container in which reconstitution of the protein is to be carried out in order to avoid a transfer step. The container in this instance may, for example, be a 3, 5, 10, 20, 50 or 100 cc vial. As a general proposition, lyophilization will result in a lyophilized formulation in which the moisture content thereof is less than about 5%, and preferably less than about 3%.

At the desired stage, typically when it is time to administer the formulation to the patient, the lyophilized formulation may be reconstituted with a diluent such that the Binding Agent concentration in the reconstituted formulation is preferably similar to that of the pre-lyophilized formulation.

Reconstitution generally takes place at a temperature of about 25° C. to ensure complete hydration, although other temperatures may be employed as desired. The time required for reconstitution will depend, e.g., on the type of diluent, amount of excipient(s) and protein. Exemplary diluents include sterile water, bacteriostatic water for injection (BWFI), a pH buffered solution (e.g. phosphate-buffered saline), sterile saline solution, Ringer's solution or dextrose solution. The diluent optionally contains a preservative. Exemplary preservatives have been described above, with aromatic alcohols such as benzyl or phenol alcohol being the preferred preservatives. The amount of preservative employed is determined by assessing different preservative concentrations for compatibility with the protein and preservative efficacy testing. For example, if the preservative is an aromatic alcohol (such as benzyl alcohol), it can be present in an amount from about 0.1-2.0% and preferably from about 0.5-1.5%, but most preferably about 1.0-1.2%.

Alternatively, a non-lyophilized formulation may be used, including a binding agent, and any of the well-known carriers, excipients, buffers, stabilizers, preservatives, adjuvants and other additives described herein and well known in the art.

Detection Assays

Provided methods permit detection of complex formation between a binding agent and S-ECD-PFS. Detection of the complexes may be achieved by any available method, e.g., an enzyme-linked immunosorbent assay (ELISA). For example, in some embodiments, an antibody to S-ECD-PFS is used. In some embodiments, a secondary antibody, e.g., an anti-S-ECD-PFS antibody is used. One or more antibodies may be coupled to a detection moiety. In some embodiments, a detection moiety is or comprises a fluorophore. As used herein, the term “fluorophore” (also referred to as “fluorescent label” or “fluorescent dye”) refers to moieties that absorb light energy at a defined excitation wavelength and emit light energy at a different wavelength. In some embodiments, a detection moiety is or comprises an enzyme. In some embodiments, an enzyme is one (e.g., ß-galactosidase) that produces a colored product from a colorless substrate.

As used herein, the terms “measuring” or “measurement,” or alternatively “detecting” or “detection,” means assessing the presence, absence, quantity or amount (which can be an effective amount) of a substance within a sample, including the derivation of qualitative or quantitative concentration levels of such substances, or otherwise evaluating the values or categorization of a subject's.

In some embodiments, a test is performed by adding capture agent to a substrate, e.g., a reaction vessel, under conditions such that the capture agent binds to the substrate, e.g., using an ELISA. A sample, e.g., tissue sample from a subject, blood, plasma, saliva or tears, may be added to the capture-agent containing substrate in a reaction vessel. Any capture agent-binding molecules present may bind to the immobilized capture agent molecules. An antibody or an antibody-detection agent conjugate may be added to the reaction mixture. The antibody part of the conjugate binds to any antigen molecules, creating an antibody-antigen-antibody “sandwich.” After washing away any unbound conjugate, a substrate solution may be added to aid in detection. For example, after a set interval, the reaction may be stopped (e.g., by adding 1 N NaOH) and the concentration of colored product formed may be measured in a spectrophotometer. The intensity of color is proportional to the concentration of bound antigen.

Examples and Experiments

It has been predicted the S protein contains a furin cleavage site between R⁶⁸² and S⁶⁸⁶ (⁶⁸²RRAR↓S⁶⁸⁶), as shown in FIG. 1. The following experiments were carried out to verify furin's role in S protein cleavage.

S-ECD is Proteolytically Cleaved into Three Bands in Wild-Type HEK293 Cells

To generate recombinant S-ECD proteins for uses in antibody development, first, a recombinant S-ECD having a 6-member Histamine tag protein at the C terminus (“5-ECD-C6×His”) was produced in HEK293 cells, then purified using a nickel column. Three bands were observed for the wild-type S-ECD-C6×His following expression, purification and separation using SDS-PAGE. As predicted, the results indicated that the S protein contains a furin cleavage site between amino acid R682 and amino acid S686 (⁶⁸²RRAR↓S⁶⁸⁶). See FIG. 1. As shown in FIG. 2, the 180 KD band corresponds to S-ECD-PFS and the 120 KD and 80 KD bands seem to correspond to the mature/active form of the S protein containing the S1 and S2 subunits.

However, the yield was low and the protein is not stable. The yield of S-ECD in HEK293 wild-type cells is generally much lower (less than 1 mg/1). Most of the recombinant S-ECDs on the market (referred to as S-ECD-MT) has a mutated cleavage site region, as shown in FIG. 1 (⁶⁸²RAAA↓S⁶⁸⁶), in order to generate a product mimicking S-ECD-PFS, and to thereby avoid protease cleavage. However, the artificial mutation/deletion also generated an irrelevant epitope and is potentially less useful in research or therapy. In addition, because of the mutation, the conventional recombinant protein is not suitable for further processing to generate an active form of furin.

Generation of Furin Gene KO Cells in HEK293 Cells by CRISPR

On the hypothesis that knocking out the FURIN gene in HEK293 cells and then expressing S-ECD in the KO in HEK293 cells would generate an intact furin protein, CRISPR-Cas9 was employed to generate the KO HEK293 cells. Two sgRNAs were designed to target exon 1. Single clones were selected and the genomic DNA was sequenced and analyzed. Two clones were sequenced which both had a 56 bp deletion resulting in a frame-shift. The KO and WT sequences of furin in the relevant regions are depicted in FIG. 3 a.

Furin protein was assayed by Western Blot; and as expected, was no longer present in the media from the KO HEK293 cells, as shown in FIG. 3 b.

Increased Yield of S-ECD in HEK293 FURIN Gene KO Cells

The same construct of the S-ECD gene generating S-ECD-C6×His was transfected into HEK293 wild type and Furin−/− cells. The conditioned media containing S-ECD-C6×His was separated by SDS-PAGE and detected by Western Blot, using an anti-6×His antibody. As expected, recombinant S-ECD showed two bands in HEK293 wild type cells, one being the full-length S-ECD and the other being S2, whereas recombinant S-ECD showed a single band in furin−/− cells. Result are shown in FIG. 3 c.

To scale up the culture and transfection in furin−/− cells, conditioned media was collected to 1 L and proteins were purified with a nickel column. The yield of S-ECD-PFS was much higher in furin−/− cells compared with wild type HEK293 cells (>20 mg/l culture). Results are shown in FIG. 4.

S-ECD-PFS has Higher ACE2 Binding Affinity than S-ECD-MT

An enzyme-linked immunosorbent assay (ELISA) was used to measure and quantify the binding activity between the S-ECDs or recombinant S1 and ACE2.

Recombinant S-ECDs and recombinant S1 (as a control) were immobilized at 2 μg/mL (100 μL/well) to a 96 well plate. Recombinant ACE2 with an added Fc domain was added to the wells by 5-fold serial dilution, from 2 μg/mL (100/well), 6 times, and a blank was used as a negative control. Captured recombinant ACE2-Fc was measured by anti-human Fc-HRP antibody. The OD was measured and the EC50 was calculated by Origin8 software. The EC50 of S1 was 12.14 ng/mL. The EC50 of S-ECD-MT was 10.38 ng/mL. The EC50 of S-ECD-PFS was 4.33 ng/mL. Lower EC50 indicates the increased binding activity, as shown in FIG. 5.

These results indicate S-ECD-PFS has higher affinity and is superior to S1 or S-ECD-MT for use as an antigen to generate antibodies or for use in detection assays or in diagnosis, as a therapeutic to interfere with SARS-CoV-2 cellular binding, or as a vaccine (to generate antibodies to SARS-CoV-2).

DETAILED METHODS

The CRISPR Cas9 protocol used the following sgRNAs:

sgRNA1: (SEQ ID NO: 19) GATGCGCACAGCCCACGTGT sgRNA2: (SEQ ID NO: 20) ACAGTGTGGCACGGAAGCAT incorporated into in the vector: £°PX459£¬addgene #62988 (from Addgene, Watertown Mass.) at the Bbs1 site. The forward and reverse sgRNA constructs (with vectors) are shown below:

Vector-sgRNA1 (forward): (SEQ ID NO: 5) £°CACC-GATGCGCACAGCCCACGTGT Vector-sgRNA1 (reverse): (SEQ ID NO: 6) £°AAAC-ACACGTGGGCTGTGCGCATC Vector-sgRNA2 (forward): (SEQ ID NO: 7) £°CACC-ACAGTGTGGCACGGAAGCAT Vector-sgRNA2 (reverse): (SEQ ID NO: 8) £°AAAC-ATGCTTCCGTGCCACACTGT

For mammalian cell transfection and protein purification, plasmid preparation was in accordance with the following exemplary protocol.

Plasmids all carry a betalactamase (amp) resistance gene and are grown in E. coli at 37° C. (or 30° C.) in shaker flasks overnight. High quality plasmid DNA can be obtained using commercially available Maxiprep kits (Qiagen), preferably including an endotoxin removal step.

HEK293 cells were adapted to Expi293 Expression Medium. The media and transfection agents below were used in a standard protocol with the equipment below, but other cell lines (including 293T, CHO etc.) with other media and transfection reagents can also be used.

Materials and Equipment

-   -   Expi293 Expression Medium (Gibco #A1435102)     -   Opti-MEM I Reduced Serum Medium (Gibco #31985088)     -   ExpiFectamine 293 Transfection Kit (Gibco #A14524)     -   PBS (1×) (Gibco #10010-023 or equivalent)     -   Ni-NTA Agarose (Qiagen #30230 or equivalent)     -   NuPAGE 4-12% Bis-Tris Protein Gels (Invitrogen Catalog number:         NP0329BOX)     -   SDS-PAGE cell and power supply     -   Sodium Chloride NaCl (Sigma-Aldrich #S3014 or equivalent)     -   Imidazole (Sigma-Aldrich #I5513 or equivalent)     -   Furin mAb antibody (Abclonal A5043)     -   Actin mAb antibody (Abclonal AC026)     -   Recombinant S-ECD R683A, R685A mutation (Abclonal RP01260MT)     -   Recombinant ACE2 (Abclonal RP01275)

Purification was performed with a nickel column (though other protein purification methods can also be used).

Sequences Wild type FURIN gene locus: part of NCBI Reference Sequence: NC_000015.10 (SEQ ID NO: 9) cctgcccgtctcggccccatgcccccaccagtcagccccgggccacaggcagtgagcaggcacctgggagccgaggc cctgtgaccaggccaaggagacgggcgctccagggtcccagccacctgtcccccccatggagctgaggccctggagct atgggtggtagcagcaacaggaaccaggtcctgctagcagctgatgctcagggccagaaggtcttcaccaacacgtggg ctgtgcgcatccctggaggcccagcggtggccaacagtgtggcacggaagcatgggacctcaacctgggccaggtagg tgacccccacaggacactgccagggggtgggaccagagaagacagggattctgggagcaggagctgaggccttgatg ctcaggggcatctgggtagccggcatgactgggtggccatgagcaaagcacaggtggttcaggcaagcagca FURIN gene genomic sequencing primers seq-F : (SEQ ID NO: 10) TCCTCTCAGGGTCGGCACTC, seq-R : (SEQ ID NO: 11) GCTGCTTGCCTGAACCACCT FURIN gene locus after KO (SEQ ID NO: 12) cgtctcggccccatgcccccaccagtcagccccgggccacaggcagtgagcaggcacctgggagccgaggccctgtg accaggccaaggagacgggcgctccagggtcccagccacctgtcccccccatggagctgaggccctggagctatgggt ggtagcagcaacaggaaccaggtcctgctagcagctgatgctcagggccagaaggtatcaccaacacatgggacctca acctgggccaggtaggtgacccccacaggacactgccagggggtgggaccagagaagacagggattctgggagcag gagctgttggccttgtttgctcaggggcatctgggtagccggcatgttctgggtggccatgagcaaagcacaggtggttca ggcaagcagca Furin-WT-protein sequence (SEQ ID NO: 13) MELRPWLLWVVAATGTLVLLAADAQGQKVFTNTWAVRIPGGPAVANSVARK HGFLNLGQIFGDYYHFWHRGVTKRSLSPHRPRHSRLQREPQVQWLEQQVAK RRTKRDVYQEPTDPKFPQQWYLSGVTQRDLNVKAAWAQGYTGHGIVVSILD DGIEKNHPDLAGNYDPGASFDVNDQDPDPQPRYTQMNDNRHGTRCAGEVAA VANNGVCGVGVAYNARIGGVRMLDGEVTDAVEARSLGLNPNHIHIYSASWGP EDDGKTVDGPARLAEEAFFRGVSQGRGGLGSIFVWASGNGGREHDSCNCDG YTNSIYTLSISSATQFGNVPWYSEACSSTLATTYSSGNQNEKQIVTTDLRQKCT ESHTGTSASAPLAAGIIALTLEANKNLTWRDMQHLVVQTSKPAHLNANDWAT NGVGRKVSHSYGYGLLDAGAMVALAQNWTTVAPQRKCIIDILTEPKDIGKRL EVRKTVTACLGEPNHITRLEHAQARLTLSYNRRGDLAIHLVSPMGTRSTLLAA RPHDYSADGFNDWAFMTTHSWDEDPSGEWVLEIENTSEANNYGTLTKFTLVL YGTAPEGLPVPPESSGCKTLTSSQACVVCEEGFSLHQKSCVQHCPPGFAPQVL DTHYSTENDVETIRASVCAPCHASCATCQGPALTDCLSCPSHASLDPVEQTCS RQSQSSRESPPQQQPPRLPPEVEAGQRLRAGLLPSHLPEVVAGLSCAFIVLVFV TVFLVLQLRSGFSFRGVKVYTMDRGLISYKGLPPEAWQEECPSDSEEDEGRGE RTAFIKDQSAL Furin-Mutation-protein sequence MELRPWLLWVVAATGTLVLLAADAQGQKVFTNTW (SEQ ID NO: 14)* frame shift S-ECD coding sequence S-ECD (AA Val16-Gln1208 (SEQ ID NO: 15)) subcloned into pcDNA vector by 5′XbaI/3′AgeI, after optimization (Accession #YP_009724390.1) gtgaacctgaccaccaggacccaacttcctcctgcctacaccaactccttcaccaggggagtctactaccctgacaaggtgt tcaggtcctctgtgctgcacagcacccaggacctgttcctgccattcttcagcaatgtgacctggttccatgccatccatgtgt ctggcaccaatggcaccaagaggtttgacaaccctgtgctgccattcaatgatggagtctactttgccagcacagagaaga gcaacatcatcaggggctggatttttggcaccaccctggacagcaagacccagtccctgctgattgtgaacaatgccacca atgtggtgattaaggtgtgtgagttccagttctgtaatgacccattcctgggagtctactaccacaagaacaacaagtcctgg atggagtctgagttcagggtctactcctctgccaacaactgtacctttgaatatgtgagccaaccattcctgatggacttggag ggcaagcagggcaacttcaagaacctgagggagtttgtgttcaagaacattgatggctacttcaagatttacagcaaacaca caccaatcaacctggtgagggacctgccacagggcttctctgccttggaaccactggtggacctgccaattggcatcaaca tcaccaggttccagaccctgctggctctgcacaggtcctacctgacacctggagactcctcctctggctggacagcaggag cagcagcctactatgtgggctacctccaaccaaggaccttcctgctgaaatacaatgagaatggcaccatcacagatgctgt ggactgtgccctggacccactgtctgagaccaagtgtaccctgaaatccttcacagtggagaagggcatctaccagacca gcaacttcagggtccaaccaacagagagcattgtgaggtttccaaacatcaccaacctgtgtccatttggagaggtgttcaat gccaccaggtttgcctctgtctatgcctggaacaggaagaggattagcaactgtgtggctgactactctgtgctctacaactc tgcctccttcagcaccttcaagtgttatggagtgagcccaaccaaactgaatgacctgtgtttcaccaatgtctatgctgactc ctttgtgattaggggagatgaggtgagacagattgcccctggacaaacaggcaagattgctgactacaactacaaactgcc tgatgacttcacaggctgtgtgattgcctggaacagcaacaacctggacagcaaggtgggaggcaactacaactacctcta cagactgacaggaagagcaacctgaaaccatttgagagggacatcagcacagagatttaccaggctggcagcacaccat gtaatggagtggagggcttcaactgttactaccactccaatcctatggatccaaccaaccaatggagtgggctaccaacca tacagggtggtggtgctgtcattgaactgctccatgcccctgccacagtgtgtggaccaaagaagagcaccaacctggtg aagaacaagtgtgtgaacttcaacttcaatggactgacaggcacaggagtgctgacagagagcaacaagaagacctgcc attccaacagtaggcagggacattgctgacaccacagatgctgtgagggacccacagaccaggagattctggacatcac accatgacctaggaggagtgtctgtgattacacctggcaccaacaccagcaaccaggtggctgtgctctaccaggatgtg aactgtactgaggtgcctgtggctatccatgctgaccaacttacaccaacctggagggtctacagcacaggcagcaatgtgt tccagaccagggctggctgtctgattggagcagagcatgtgaacaactcctatgagtgtgacatcccaattggagcaggca tctgtgcctcctaccagacccagaccaacagcccaaggagggcaaggtctgtggcaagccagagcatcattgcctacaca atgagtctgggagcagagaactctgtggcttacagcaacaacagcattgccatcccaaccaacttcaccatctctgtgacca cagagattctgcctgtgagtatgaccaagacctctgtggactgtacaatgtatatctgtggagacagcacagagtgtagcaa cctgctgctccaatatggctccactgtacccaacttaacagggctctgacaggcattgctgtggaacaggacaagaacacc caggaggtgatgcccaggtgaagcagatttacaagacacctccaatcaaggactaggaggcttcaacttcagccagattc tgcctgacccaagcaagccaagcaagaggtcatcattgaggacctgctgacaacaaggtgaccctggctgatgctggct tcatcaagcaatatggagactgtctgggagacattgctgccagggacctgatagtgcccagaagttcaatggactgacagt gctgcctccactgctgacagatgagatgattgcccaatacacctctgccctgctggctggcaccatcacctctggctggacc taggagcaggagcagccctccaaatcccatttgctatgcagatggcttacaggacaatggcattggagtgacccagaatgt gctctatgagaaccagaaactgattgccaaccagttcaactctgccattggcaagattcaggactccctgtccagcacagcc tctgccctgggcaaactccaagatgtggtgaaccagaatgcccaggctctgaacaccctggtgaagcaactaccagcaac taggagccatctcctctgtgctgaatgacatcctgagcagactggacaaggtggaggctgaggtccagattgacagactg attacaggcagactccaatccctccaaacctatgtgacccaacaacttatcagggctgctgagattagggcatctgccaacc tggctgccaccaagatgagtgagtgtgtgctgggacaaagcaagagggtggacactgtggcaagggctaccacctgatg agattccacagtctgcccctcatggagtggtgacctgcatgtgacctatgtgcctgcccaggagaagaacttcaccacagc ccctgccatctgccatgatggcaaggctcactaccaagggagggagtgatgtgagcaatggcacccactggtagtgacc cagaggaacactatgaaccacagattatcaccacagacaacacctagtgtctggcaactgtgatgtggtgattggcattgtg aacaacacagtctatgacccactccaacctgaactggactcatcaaggaggaactggacaaatacttcaagaaccacacc agccctgatgtggacctgggagacatctctggcatcaatgcctctgtggtgaacatccagaaggagattgacagactgaat gaggtggctaagaacctgaatgagtccctgattgacctccaagaactgggcaaatatgaacaatacatcaagtggccacat catcaccaccatcactaa S-ECD (AA Val16-Gln1208 (SEQ ID NO: 16)) Protein sequence VNLTTRTQLPPAYTNSFTRGVYYPDKVFRSSVLHSTQDLFLPFFSNVTWFHAIH VSGTNGTKRFDNPVLPFNDGVYFASTEKSNIIRGWIFGTTLDSKTQSLLIVNNA TNVVIKVCEFQFCNDPFLGVYYHKNNKSWMESEFRVYSSANNCTFEYVSQPF LMDLEGKQGNFKNLREFVFKNIDGYFKIYSKHTPINLVRDLPQGFSALEPLVD LPIGINITRFQTLLALHRSYLTPGDSSSGWTAGAAAYYVGYLQPRTFLLKYNEN GTITDAVDCALDPLSETKCTLKSFTVEKGIYQTSNFRVQPTESIVRFPNITNLCP FGEVFNATRFASVYAWNRKRISNCVADYSVLYNSASFSTFKCYGVSPTKLNDL CFTNVYADSFVIRGDEVRQIAPGQTGKIADYNYKLPDDFTGCVIAWNSNNLDS KVGGNYNYLYRLFRKSNLKPFERDISTEIYQAGSTPCNGVEGFNCYFPLQSYG FQPTNGVGYQPYRVVVLSFELLHAPATVCGPKKSTNLVKNKCVNFNFNGLTG TGVLTESNKKFLPFQQFGRDIADTTDAVRDPQTLEILDITPCSFGGVSVITPGTN TSNQVAVLYQDVNCTEVPVAIHADQLTPTWRVYSTGSNVFQTRAGCLIGAEH VNNSYECDIPIGAGICASYQTQTNSPRRARSVASQSIIAYTMSLGAENSVAYSN NSIAIPTNFTISVTTEILPVSMTKTSVDCTMYICGDSTECSNLLLQYGSFCTQLN RALTGIAVEQDKNTQEVFAQVKQIYKTPPIKDFGGFNFSQILPDPSKPSKRSFIE DLLFNKVTLADAGFIKQYGDCLGDIAARDLICAQKFNGLTVLPPLLTDEMIAQ YTSALLAGTITSGWTFGAGAALQIPFAMQMAYRFNGIGVTQNVLYENQKLIA NQFNSAIGKIQDSLSSTASALGKLQDVVNQNAQALNTLVKQLSSNFGAISSVL NDILSRLDKVEAEVQIDRLITGRLQSLQTYVTQQLIRAAEIRASANLAATKMSE CVLGQSKRVDFCGKGYHLMSFPQSAPHGVVFLHVTYVPAQEKNFTTAPAICH DGKAHFPREGVFVSNGTHWFVTQRNFYEPQIITTDNTFVSGNCDVVIGIVNNT VYDPLQPELDSFKEELDKYFKNHTSPDVDLGDISGINASVVNIQKEIDRLNEVA KNLNESLIDLQELGKYEQHHHHHH 6. S-ECD cloning sequence S-ECD (AA Met1 -Gln1208 (SEQ ID NO: 17)) which was subcloned into pcDNA vector by 5′XbaI/3′AgeI; includes the optimized DNA codon; with the underlined signal peptide coding section (Accession #YP_009724390.1) atgtttgtgttcctggtgctgctgccactggtgtccagccagtgtgtgaacctgaccaccaggacccaacttcctcctgcctac accaactccttcaccaggggagtctactaccctgacaaggtgttcaggtcctctgtgctgcacagcacccaggacctgttcc tgccattcttcagcaatgtgacctggttccatgccatccatgtgtctggcaccaatggcaccaagaggtttgacaaccctgtg ctgccattcaatgatggagtctactttgccagcacagagaagagcaacatcatcaggggctggatttttggcaccaccctgg acagcaagacccagtccctgctgattgtgaacaatgccaccaatgtggtgattaaggtgtgtgagttccagttctgtaatgac ccattcctgggagtctactaccacaagaacaacaagtcctggatggagtctgagttcagggtctactcctctgccaacaact gtacctttgaatatgtgagccaaccattcctgatggacttggagggcaagcagggcaacttcaagaacctgagggagtttgt gttcaagaacattgatggctacttcaagatttacagcaaacacacaccaatcaacctggtgagggacctgccacagggcttc tctgccttggaaccactggtggacctgccaattggcatcaacatcaccaggttccagaccctgctggctctgcacaggtcct acctgacacctggagactcctcctctggctggacagcaggagcagcagcctactatgtgggctacctccaaccaaggacc hcctgctgaaatacaatgagaatggcaccatcacagatgctgtggactgtgccctggacccactgtctgagaccaagtgta ccctgaaatccttcacagtggagaagggcatctaccagaccagcaacttcagggtccaaccaacagagagcattgtgagg tttccaaacatcaccaacctgtgtccatttggagaggtgttcaatgccaccaggtttgcctctgtctatgcctggaacaggaag aggattagcaactgtgtggctgactactctgtgctctacaactctgcctccttcagcaccttcaagtgttatggagtgagccca accaaactgaatgacctgtgtttcaccaatgtctatgctgactcattgtgattaggggagatgaggtgagacagattgcccct ggacaaacaggcaagattgctgactacaactacaaactgcctgatgacttcacaggctgtgtgattgcctggaacagcaac aacctggacagcaaggtgggaggcaactacaactacctctacagactgttcaggaagagcaacctgaaaccatttgagag ggacatcagcacagagatttaccaggctggcagcacaccatgtaatggagtggagggcttcaactgttactuccactccaa tcctatggcttccaaccaaccaatggagtgggctaccaaccatacagggtggtggtgctgtcctttgaactgctccatgccc ctgccacagtgtgtggaccaaagaagagcaccaacctggtgaagaacaagtgtgtgaacttcaacttcaatggactgaca ggcacaggagtgctgacagagagcaacaagaagttcctgccattccaacagtttggcagggacattgctgacaccacaga tgctgtgagggacccacagaccttggagattctggacatcacaccatgttcctttggaggagtgtctgtgattacacctggca ccaacaccagcaaccaggtggctgtgctctaccaggatgtgaactgtactgaggtgcctgtggctatccatgctgaccaact tacaccaacctggagggtctacagcacaggcagcaatgtgttccagaccagggctggctgtctgattggagcagagcatg tgaacaactcctatgagtgtgacatcccaattggagcaggcatctgtgcctcctaccagacccagaccaacagcccaagga gggcaaggtctgtggcaagccagagcatcattgcctacacaatgagtctgggagcagagaactctgtggcttacagcaac aacagcattgccatcccaaccaacttcaccatctctgtgaccacagagattctgcctgtgagtatgaccaagacctctgtgga ctgtacaatgtatatctgtggagacagcacagagtgtagcaacctgctgctccaatatggctccttctgtacccaacttaacag ggctctgacaggcattgctgtggaacaggacaagaacacccaggaggtgtttgcccaggtgaagcagatttacaagacac ctccaatcaaggactttggaggcttcaacttcagccagattctgcctgacccaagcaagccaagcaagaggtccttcattga ggacctgctgttcaacaaggtgaccctggctgatgctggcttcatcaagcaatatggagactgtctgggagacattgctgcc agggacctgatttgtgcccagaagttcaatggactgacagtgctgcctccactgctgacagatgagatgattgcccaataca cctctgccctgctggctggcaccatcacctctggctggacctttggagcaggagcagccctccaaatcccatttgctatgca gatggcttacaggttcaatggcattggagtgacccagaatgtgctctatgagaaccagaaactgattgccaaccagttcaac tctgccattggcaagattcaggactccctgtccagcacagcctctgccctgggcaaactccaagatgtggtgaaccagaat gcccaggctctgaacaccctggtgaagcaactttccagcaactttggagccatctcctctgtgctgaatgacatcctgagca gactggacaaggtggaggctgaggtccagattgacagactgattacaggcagactccaatccctccaaacctatgtgacc caacaacttatcagggctgctgagattagggcatctgccaacctggctgccaccaagatgagtgagtgtgtgctgggacaa agcaagagggtggacttctgtggcaagggctaccacctgatgagttttccacagtctgcccctcatggagtggtgttcctgc atgtgacctatgtgcctgcccaggagaagaacttcaccacagcccctgccatctgccatgatggcaaggctcactttccaag ggagggagtgtttgtgagcaatggcacccactggtttgtgacccagaggaacttctatgaaccacagattatcaccacaga caacacctttgtgtctggcaactgtgatgtggtgattggcattgtgaacaacacagtctatgacccactccaacctgaactgg actccttcaaggaggaactggacaaatacttcaagaaccacaccagccctgatgtggacctgggagacatctctggcatca atgcctctgtggtgaacatccagaaggagattgacagactgaatgaggtggctaagaacctgaatgagtccctgattgacct ccaagaactgggcaaatatgaacaatacatcaagtggccacatcatcaccaccatcactaa Protein sequence (AA Met1-Gln1208(SEQ ID NO: 18)), with signal peptide underlined MFVFLVLLPLVSSQCVNLTTRTQLPPAYTNSFTRGVYYPDKVFRSSVLHSTQDL FLPFFSNVTWFHAIHVSGTNGTKRFDNPVLPFNDGVYFASTEKSNIIRGWIFGT TLDSKTQSLLIVNNATNVVIKVCEFQFCNDPFLGVYYHKNNKSWMESEFRVY SSANNCTFEYVSQPFLMDLEGKQGNFKNLREFVFKNIDGYFKIYSKHTPINLV RDLPQGFSALEPLVDLPIGINITRFQTLLALHRSYLTPGDSSSGWTAGAAAYYV GYLQPRTFLLKYNENGTITDAVDCALDPLSETKCTLKSFTVEKGIYQTSNFRV QPTESIVRFPNITNLCPFGEVFNATRFASVYAWNRKRISNCVADYSVLYNSASFS TFKCYGVSPTKLNDLCFTNVYADSFVIRGDEVRQIAPGQTGKIADYNYKLPDD FTGCVIAWNSNNLDSKVGGNYNYLYRLFRKSNLKPFERDISTEIYQAGSTPCN GVEGFNCYFPLQSYGFQPTNGVGYQPYRVVVLSFELLHAPATVCGPKKSTNL VKNKCVNFNFNGLTGTGVLTESNKKFLPFQQFGRDIADTTDAVRDPQTLEILDI TPCSFGGVSVITPGTNTSNQVAVLYQDVNCTEVPVAIHADQLTPTWRVYSTGS NVFQTRAGCLIGAEHVNNSYECDIPIGAGICASYQTQTNSPRRARSVASQSIIA YTMSLGAENSVAYSNNSIAIPTNFTISVTTEILPVSMTKTSVDCTMYICGDSTEC SNLLLQYGSFCTQLNRALTGIAVEQDKNTQEVFAQVKQIYKTPPIKDFGGFNFS QILPDPSKPSKRSFIEDLLFNKVTLADAGFIKQYGDCLGDIAARDLICAQKFNG LTVLPPLLTDEMIAQYTSALLAGTITSGWTFGAGAALQIPFAMQMAYRFNGIG VTQNVLYENQKLIANQFNSAIGKIQDSLSSTASALGKLQDVVNQNAQALNTL VKQLSSNFGAISSVLNDILSRLDKVEAEVQIDRLITGRLQSLQTYVTQQLIRAA EIRASANLAATKMSECVLGQSKRVDFCGKGYHLMSFPQSAPHGVVFLHVTYV PAQEKNFTTAPAICHDGKAHFPREGVFVSNGTHWFVTQRNFYEPQIITTDNTF VSGNCDVVIGIVNNTVYDPLQPELDSFKEELDKYFKNHTSPDVDLGDISGINA SVVNIQKEIDRLNEVAKNLNESLIDLQELGKYEQHHHHHH

The specific methods and compositions described herein are representative of preferred embodiments and are exemplary and not intended as limitations on the scope of the invention. Other objects, aspects, and embodiments will occur to those skilled in the art upon consideration of this specification, and are encompassed within the spirit of the invention as defined by the scope of the claims. It will be readily apparent to one skilled in the art that varying substitutions and modifications may be made to the invention disclosed herein without departing from the scope and spirit of the invention. The invention illustratively described herein suitably may be practiced in the absence of any element or elements, or limitation or limitations, which is not specifically disclosed herein as essential. Thus, for example, in each instance herein, in embodiments or examples of the present invention, any of the terms “comprising”, “including”, containing”, etc. are to be read expansively and without limitation. The methods and processes illustratively described herein suitably may be practiced in differing orders of steps, and that they are not necessarily restricted to the orders of steps indicated herein or in the claims. It is also noted that as used herein and in the appended claims, the singular forms “a,” “an,” and “the” include plural reference, and the plural include singular forms, unless the context clearly dictates otherwise. Under no circumstances may the patent be interpreted to be limited to the specific examples or embodiments or methods specifically disclosed herein. Under no circumstances may the patent be interpreted to be limited by any statement made by any Examiner or any other official or employee of the Patent and Trademark Office unless such statement is specifically and without qualification or reservation expressly adopted in a responsive writing by Applicants.

The invention has been described broadly and generically herein. Each of the narrower species and subgeneric groupings falling within the generic disclosure also form part of the invention. The terms and expressions that have been employed are used as terms of description and not of limitation, and there is no intent in the use of such terms and expressions to exclude any equivalent of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the invention as claimed. Thus, it will be understood that although the present invention has been specifically disclosed by preferred embodiments and optional features, modification and variation of the concepts herein disclosed may be resorted to by those skilled in the art, and that such modifications and variations are considered to be within the scope of this invention as defined by the appended claims.

REFERENCES

-   1. Coutard B, Valle C, de Lamballerie X, Canard B, Seidah N G,     Decroly E. The spike glycoprotein of the new coronavirus 2019-nCoV     contains a furin-like cleavage site absent in CoV of the same Glade.     Antiviral Res. 2020; 176:104742. doi:10.1016/j.antiviral.2020.104742 -   2. Hoffmann M, Kleine-Weber H, Schroeder S, et al. SARS-CoV-2 Cell     Entry Depends on ACE2 and TMPRSS2 and Is Blocked by a Clinically     Proven Protease Inhibitor. Cell. 2020; 181(2):271-280.e8.     doi:10.1016/j.cell.2020.02.052 -   3. Furin See Wikipedia Website -   4. Stadlbauer D, Amanat F, Chromikova V, et al. SARS-CoV-2     Seroconversion in Humans: A Detailed Protocol for a Serological     Assay, Antigen Production, and Test Setup. Curr Protoc Microbiol.     2020; 57(1):e100. doi:10.1002/cpmc.100 

1-20. (canceled)
 21. A process of generating the mature, active form of the SARS-CoV-2 S protein comprising cleaving the unmutated pre-fusion form of S protein with furin at a cleavage site between amino acid Arginine 682 and amino acid Serine 686 to yield the mature, active form of SARS Cov2 S protein containing the S1 and S2 subunits.
 22. The process of claim 1 wherein the cleavage site is between Arginine 685 and Serine
 686. 23. The process of claim 1 wherein the cleavage site is between Arginine 670 and Serine 671 in the extracellular domain shown in SEQ ID NO.:
 16. 